Why does the object turn black in the Edit Mode?
You have an extremely large number of faces (and edges, and vertices). If you hit 'A' a few times in edit mode it will toggle orange/black/orange, etc.

Depending on what you intend to use this for, it may be far too many faces.

It is possible that you have a subdivision-surface modifier on this object, and the 'view subdivision' count is too high. Check your Modifiers tab to find out.